1. Field of the Invention
The invention pertains generally to archery bows. More particularly, the invention relates to an archery bow which utilizes the full length of the limbs to activate a power unit that transfers energy to an arrow upon release of the bow string.
Traditionally, archery bows are formed as a unitary structure having limbs which possess a resistance to bending when a bow string extending between the limbs is pulled back in a direction away from the bow. When the bow string is drawn back, the limbs are deformed, behaving essentially as springs whereby energy is created and stored in the deformed limbs. When the bow string is released, the limbs are restored to their original unflexed position, and the stored energy of the limbs is released, thereby causing straightening of the bow string and propulsion of an arrow which is mounted on the string.
Bows of the foregoing type are generally characterized by the limb members being utilized to deform another portion of the limb members upon retraction of the bow spring, and thus require a high pull force on the bow string in order to achieve high speed and long range for the arrow. Additionally, bows of the latter type must possess a uniform spring rate in order to obtain consistent accuracy and a uniform propelling force upon the arrow.
Archery bows wherein a significant portion of the limbs is deflected in order to transmit a greater reaction propelling force to the string and, hence, the arrow, are costly and difficult to fabricate. The need to establish a uniform spring rate in the limbs further increases the costs of construction for such archery bows.
Prior art efforts to enhance the restoring force which the limbs exert on the bow string have generally involved the addition of extraneous elements at the string end of the limbs. These elements, such as pulleys, camming devices and the like, add to the complexity and manufacturing costs for the bow.
Thus, the need exists for an archery bow which effectively reduces the pull force required for the bow, while substantially increasing the restoring force transferred to the arrow upon release of the bow string in a consistently accurate manner. Additionally, the need exists for a bow having the latter attributes, and which is simple, economical, and conducive to manufacture.
The subject invention realizes the foregoing objects and benefits by providing an archery bow wherein the entire length of the bow's limbs is utilized as a lever to activate a power unit associated with the limbs opposite the string ends of the limbs. The pull force imposed on the bow string by a user is directed to rotate the limbs solely to activate the power unit, rather than to bend the limbs themselves in order to create a reaction force as with conventional archery bows.
The power unit of the present invention comprises a pair of spring members, one for each limb, which are energized by the mechanical lever-action of the limbs when the bow string is drawn. Upon release of the bow string, the restoring force which the power unit spring exerts on the limbs causes the limbs to restore the bow string to a taut position and project an associated arrow. The length of the limbs and the strength of the springs may be varied to obtain diverse power and pull characteristics. Because the entire length of the limbs is utilized as a lever to load the power unit, the archery bow of the subject invention is capable of achieving high power and speed outputs with relatively low pulling force requirements. Moreover, each limb of the archery bow of the invention activates its respective spring separately, thereby insuring uniform propelling forces on the arrow and consistent accuracy.
2. Description of the Prior Art
It is known in the prior art to provide spring members on archery bows to increase the restoring force imposed upon the bow string. U.S. Pat. No. 4,338,909, issued on July 13, 1982 to Plummer, teaches an archery bow wherein arms which are pivotally secured to the main beam member uncoil a respective spring upon drawing back of the bow string. Release of the bow string results in recoiling of the springs and simultaneous movement of the arms and, thus the bow string, to their original position. The springs, however, are secured to the string ends of their respective arms, and the arms thus do not contribute leverage action to the springs to reduce the required pull force, but serve merely to stretch the springs.
U.S. Pat. No. 3,518,980, which issued to Hamm on July 7, 1970, discloses a bow including a center section, the ends of which are adjustably secured within tubular outer sections. Each outer section has a spring disposed therein, with one end of the spring secured to its respective outer section and the other end of the spring secured to the bow string. The springs are placed in tension when the bow string is retracted, and cause straightening of the string when the string is released.
The prior art also discloses the concept of providing a spring member in the center portion of the bow. For example, U.S. Pat. No. 428,912, to Holmes, which issued on May 27, 1890, shows an archery bow having a coil spring pivotably secured to the ends of the center body of the bow. The ends of the spring are coiled to form an arm, to which the bow string is attached. The fact that the arms are formed of spring steel limits the bow to toleration of only the slightest of pulls.
Similarly, U.S. Pat. No. 1,161,642, which issued to Enos, Jr. on Nov. 23, 1915, discloses a bow fabricated entirely of spring steel and being defined by a central coil spring and a pair of spring arms. The spring arms of Enos, Jr., being made of spring steel, would suffer the same limitations as the bow of Holmes.
Finally, the bow disclosed by Zima, U.S. Pat. No. 2,116,650 dated May 10, 1938, is characterized by a centrally located spring which serves to increase, rather than decrease, the pull force required for the bow.
None of the foregoing prior art references provide or suggest the teachings for an archery bow specifically characterized by a spring-loaded power unit mounted between the riser of the bow and each of the ends of the bow limbs opposite the string in a structural arrangement which utilizes the full length of the limbs as leverage to load the power unit.